An organosiloxane having a functional group at one terminal of its molecular chain is used as a raw material of a graft organic polymer that has organosiloxane chain branches by reactivity of the functional group. The organic polymer incorporating this organosiloxane has high functions such as powder dispersibility, water repellency, antifouling property, non-adhesiveness, heat resistance, wear resistance, biocompatibility, and oxygen permeability.
It is conventionally known that the organosiloxane having a functional group at one terminal of its molecular chain can be synthesized by ring-opening polymerization of hexamethylcyclotrisiloxane, followed by capping the reaction terminal with terminating agents containing various functional groups (Patent Literature 1 and Patent Literature 2).
It is also known that an organosiloxane having a (meth)acryl group at one terminal can be synthesized by ring-opening polymerization of hexamethylcyclotrisiloxane using trimethyl silanol or 3-methacryloxypropyldimethyl silanol as an initiator in the presence of 5-coordinate silicon catalyst, followed by terminating the reaction by 3-methacryloxypropyldimethylchlorosilane or trimethylchlorosilane.
In the above method, however, the organosiloxane of the main chain is not branched and has inadequate oxygen permeability, sliding property, release property, dispersibility, and so on.
A method for synthesizing a branched siloxane is proposed in Patent Literature 3, which discloses a method for producing a branched tetrasiloxane in high yield by hydrolysis reaction in the presence of an acid catalyst. However, a method for polymerizing the siloxane has not been disclosed. Synthesis methods reported by Hrecaycho and others enable a target product to be obtained in high yield, but require a specific catalyst (Non Patent Literatures 1 and 2).
Patent Literature 4 and Patent Literature 5 propose compounds having a dendrimer structure, which are one-molecular-chain-terminal functionalized organosiloxane compounds having an extremely branched organosiloxane chain. A material using this compound is excellent in coating property, but a method for producing the same requires complicated steps and a specific starting material for synthesis.